ASP.NET - Accessing web page twice from client - asp.net

Question

What happens if one user tries to access an ASP.NET page twice before the first page is returned to the client? Have a look at the code below:
Partial Class _Default
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Session("ID") = 1
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
Response.Redirect("Default3.aspx")
End Sub End Class
Partial Class Default2
Inherits System.Web.UI.Page
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Session("ID") = 2
End Sub
Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
Response.Redirect("Default3.aspx")
End Sub
End Class
Imports System.Threading
Partial Class Default3
Inherits System.Web.UI.Page
Dim intTest As Integer = 0
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
For intTest = 0 To 10
Response.Write(Session("ID") & " " & intTest & "<br>")
Thread.Sleep(1000)
Next
End Sub
End Class
Accessing default3.axpx from the same client (PC) concurrently from default.aspx (by clicking button) and default2.aspx (by clicking button) causes the session variable to be the same on both requests (though I set the variable to 1 on the first request and 2 on the second). Is it possible to replicate this behaviour without threading? I believe I have this bug in an asp.net application that does not use threading.

Answer 1

Your question is not about multi-threading; it is about SessionState.
ASP.NET run time uses lock to avoid overriding same session variables although it can handles multiple requests.
It's why you are do not see miss-matching results.
Please also look at -
ASP.NET Application and Page Life Cycle
ASP.NET Application Life Cycle Overview

Answer 2

It's important to understand that session information is stored at the application level, and really has nothing directly to do with a page.
You could compare it to a global variable in a class. If all your methods are reading and writing to this variable, it will always contain the information from the last time it was updated. It doesn't matter how many times, or which methods, updated it.
To help see this in your code, create a new class with one property. Change your session variable to be an object of this class. Modify your session logic to refer to this object instead of a string, and update the property.
Finally, put a break point on the setter of your property.
This will let you see whenever your session variable is updated, and with what value. You can also view your stack trace to see what's setting it.
-note, this is all assuming you aren't introducing a farm into this and are accessing session from different machines--